Charge pumping DC-to-DC converters are used in power supplies in conjunction with many integrated circuits, and especially with batteries and the like. In such circuits it is not uncommon for the source of power (e.g. the battery) to vary by as much as 50%. For example, a 6 volt battery might normally not be changed until it drops as low as 3 volts.
Charge pumping DC-to-DC converters generally operate with at least two capacitors which are first connected in parallel with the power source until they are charged and are then connected in series with the power source to provide a much higher potential at an output. In this example using two capacitors, if a six volt battery is connected to the input a maximum output voltage of 18 volts is achieved. However, if the battery voltage drops to only 3 volts the maximum output drops to 9 volts.
Prior art devices compensated for such variations by converting the output to a value which would operate attached electronic circuits with the lowest acceptable potential, in the above example 9 volts. The problem with this solution is that the highest maximum output, 18 volts in the above example, is much too high. Thus, it is necessary for prior art circuits to include some voltage clamping device, such as a Zener diode, to reduce the output voltage to an acceptable level. The clamping device sinks current during the period of excess voltage to drop the voltage to the required level. Also, series pass devices, such as resistors, are used in the output of prior art converters to aid in filtering the output voltage. Because voltage is dropped across these series pass devices, it is necessary to raise the maximum voltage in the converter even higher to provide the required output voltage.
In most cases the switching of the capacitors, connections to the output terminal, etc. are accomplished by switching transistors. The extremely high voltages from the capacitors has a tendency to cause breakdowns in the switching transistors and produce latch-up and/or reliability problems. This is especially true since the geometry in semiconductor wafer processing is getting smaller and, consequently, the breakdown voltages of transistors is getting lower. As an additional problem it should also be noted that the prior art circuits waste power by sinking current to reduce the output voltage to some substantially lower value and by requiring series pass components in the output circuit.